The present study explored a key miRNA that plays a vital role in sciatic nerve conditioning injury promoting repair of injured dorsal column, and validated its function. Microarray analysis revealed miR-17-5p expression decreased sharply at 3, 7 and 14 days in the sciatic nerve conditioning injury group compared with the simple dorsal column lesion group. After miR-17-5p inhibition in DRG neurons, GAP-43 expression was upregulated and neurite growth was increased. STAT3 together with p-STAT3 showed opposite trends with miR-17-5p. MiR-17-5p inhibition extended neurite and upregulated STAT3, p-STAT3 and GAP-43. To further determine a substitution therapy for sciatic nerve conditioning injury, beta-phenethyl isothiocyanate (PEITC), which downregulates miR-17-5p, was assessed. The results showed that treatment with 10 µM PEITC resulted in longest neurite length. Further experiments demonstrated PEITC induced neurite growth by inhibiting miR-17-5p and further upregulating STAT3, p-STAT3 and GAP-43. The somatosensory evoked potential test confirmed similar treatment effects for PEITC, Ad-miRNA-17-5p inhibitor, and sciatic nerve conditioning injury on the dorsal column lesion. In conclusion, the miR-17-5p/STAT3/GAP-43 axis is an indispensable component of sciatic nerve conditioning injury promoting repair of injured dorsal column. PEITC could promote repair of injured dorsal column via the miR-17-5p/STAT3/GAP-43 axis, and could mimic the treatment effect of sciatic nerve conditioning injury.

Spinal cord injury (SCI) is a devastating disease. Strategies that enhance the intrinsic regenerative ability are very important for the recovery of SCI to radically prevent the occurrence of sensory disorders. Epidermal growth factor (EGF) showed a limited effect on the growth of primary sensory neuron neurites due to the degradation of phosphorylated-epidermal growth factor receptor (p-EGFR) in a manner dependent on Casitas B-lineage lymphoma (CBL) (an E3 ubiquitin-protein ligase). MiR-22-3p predicted from four databases could target CBL to inhibit the expression of CBL, increase p-EGFR levels and neurites length via STAT3/GAP43 pathway rather than Erk1/2 axis. EGF, EGFR, and miR-22-3p were downregulated sharply after injury. In vivo miR-22-3p Agomir application could regulate CBL/p-EGFR/p-STAT3/GAP43/p-GAP43 axis, and restore spinal cord sensory conductive function. This study clarified the mechanism of the limited promotion effect of EGF on adult primary sensory neuron neurite and targeting miR-22-3p could be a novel strategy to treat sensory dysfunction after SCI. K E Y W O R D Scasitas b-lineage lymphoma, epidermal growth factor, epidermal growth factor receptor, miR-22-3p, primary sensory neuron, spinal cord injury

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Sensory dysfunction post spinal cord injury causes patients great distress. Sciatic nerve conditioning injury (SNCI) has been shown to restore sensory function after spinal cord dorsal column injury (SDCL); however, the underlying mechanism of this recovery remains unclear. We performed a microarray assay to determine the associated miRNAs that might regulate the process of SNCI promoting SDCL repair. In total, 13 miRNAs were identified according to our inclusion criteria, and RT-qPCR was used to verify the microarray results. Among the 13 miRNAs, the miR-155-5p levels were decreased at 9 h, 3 d, 7 d, 14 d, 28 d, 2 m and 3 m timepoints in the SDCL group, while the SNCI group had a smaller decrease. Thus, miR-155-5p was chosen for further study after a literature review and an analysis with the TargetScan online tool. Specifically, miR-155-5p targets PKI-α, and the expression pattern of PKI-α was opposite that of miR-155-5p in both the SDCL and SNCI groups. Interestingly, miR-155-5p could promote dorsal root ganglion (DRG) neuron axon growth via the cAMP/PKA pathway and in a TNF-α, IL-1β or MAG inhibitory microenvironment in vitro. Furthermore, miR-155-5p could regulate the cAMP/PKA pathway and promote sensory conduction function recovery post dorsal column injury as detected by NF-200 immunohistochemistry, somatosensory-evoked potentials, BBB scale and tape removal test. Collectively, our results demonstrated that miR-155-5p participates in the molecular mechanism by which SNCI promotes the repair of SDCL and that upregulated miR-155-5p can repair SDCL by enhancing DRG neuron axon growth via the cAMP/PKA pathway. These findings suggest a novel treatment target for spinal cord injury.

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